The gating mechanism in cyclic nucleotide-gated ion channels

Monica Mazzolini,Luisa M R Napolitano,Claudio Anselmi,Arin Marchesi,Debora Grosa,Sourav Maity,Vincent Torre,Manuel Arcangeletti

doi:10.1038/s41598-017-18499-0

Abstract

Cyclic nucleotide-gated (CNG) channels mediate transduction in several sensory neurons. These channels use the free energy of CNs’ binding to open the pore, a process referred to as gating. CNG channels belong to the superfamily of voltage-gated channels, where the motion of the α-helix S6 controls gating in most of its members. To date, only the open, cGMP-bound, structure of a CNG channel has been determined at atomic resolution, which is inadequate to determine the molecular events underlying gating. By using electrophysiology, site-directed mutagenesis, chemical modification, and Single Molecule Force Spectroscopy, we demonstrate that opening of CNGA1 channels is initiated by the formation of salt bridges between residues in the C-linker and S5 helix. These events trigger conformational changes of the α-helix S5, transmitted to the P-helix and leading to channel opening. Therefore, the superfamily of voltage-gated channels shares a similar molecular architecture but has evolved divergent gating mechanisms.

Highlights

Voltage-gated ion channels form a large super-family with a common overall architecture derived from a common ancestor[1]
We used single molecule force spectroscopy (SMFS), which allows the identification of the interactions and relative motion between specific domains[25,26]. By means of this approach we identify conformational changes of S5 as an essential step for the gating of CNGA1 channels, to what is likely to occur in K+ channels gated by intracellular ions such as Ca2+ and Na+3,4
Gating of Cyclic nucleotide-gated (CNG) channels is initiated by the binding of cyclic nucleotides (CNs) to the cyclic nucleotide-binding (CNB) domain and terminates with the opening of the gate located in the pore region, approximately some tens of Å apart[10,11]

Summary

Introduction

Voltage-gated ion channels form a large super-family with a common overall architecture derived from a common ancestor[1]. This family includes usual voltage gated Na+, K+ and Ca2+ selective channels as well as other ion channels not directly gated by voltage, but by a variety of molecules and ions such as Ca2+, Na+ and cyclic nucleotide-gated (CNG) channels that are opened by the binding of cyclic nucleotides (CNs)[2,3,4,5,6] Members of this family - voltage gated K+, Na+ and Ca2+ channels in particular - have been extensively studied and it is well established that their gating is primarily controlled by the outward bending of the S6 α-helices[7,8]. Channel in the closed and unliganded state is available, and the precise mechanism of ligand-mediated activation for this class of channels remains unknown

Methods

Results

Conclusion